The table of activity-mass relationships for uranium and natural thorium are as follows:

Thorium and uranium enrichment
1(Wt%
235 U present)

Specific activity

TBq/gram

Grams/Tbq

Ci/gram

Grams/Ci

0.45 (depleted)

1.9 × 10−8

5.4 × 10
7

5.0 × 10−7

2.0 × 10
6

0.72 (natural)

2.6 × 10−8

3.8 × 10
7

7.1 × 10−7

1.4 × 10
6

1.0

2.8 × 10−8

3.6 × 10
7

7.6 × 10−7

1.3 × 10
6

1.5

3.7 × 10−8

2.7 × 10
7

1.0 × 10−6

1.0 × 10
6

5.0

1.0 × 10−7

1.0 × 10
7

2.7 × 10−6

3.7 × 10
5

10.0

1.8 × 10−7

5.6 × 10
6

4.8 × 10−6

2.1 × 10
5

20.0

3.7 × 10−7

2.7 × 10
6

1.0 × 10−5

1.0 × 10
5

35.0

7.4 × 10−7

1.4 × 10
6

2.0 × 10−5

5.0 × 10
4

50.0

9.3 × 10−7

1.1 × 10
6

2.5 × 10−5

4.0 × 10
4

90.0

2.1 × 10−6

4.7 × 10
5

5.8 × 10−5

1.7 × 10
4

93.0

2.6 × 10−6

3.9 × 10
5

7.0 × 10−5

1.4 × 10
4

95.0

3.4 × 10−6

3.0 × 10
5

9.1 × 10−5

1.1 × 10
4

Natural thorium

8.1 × 10−9

1.2 × 10
8

2.2 × 10−7

4.6 × 10
6

1 The figures for uranium include representative values for the activity of uranium-234 which is concentrated during the enrichment process. The activity for thorium includes the equilibrium concentration of thorium-228.

This final rule corrects editorial errors, makes minor regulatory changes and, in response to requests for clarification, improves the clarity of certain provisions in the Hazardous Materials Regulations. The intended effect of this rule is to enhance the accuracy and reduce misunderstandings of the regulations. The amendments contained in this rule are non-substantive changes and do not impose new requirements.

On May 8, 2015, the Pipeline and Hazardous Materials Safety Administration, in coordination with the Federal Railroad Administration (FRA), published a final rule entitled “Hazardous Materials: Enhanced Tank Car Standards and Operational Controls for High-Hazard Flammable Trains,” which adopted requirements designed to reduce the consequences and, in some instances, reduce the probability of accidents involving trains transporting large quantities of Class 3 flammable liquids. The Hazardous Materials Regulations provide a person the opportunity to appeal a PHMSA action, including a final rule. PHMSA received six appeals regarding the final rule, one of which was withdrawn. This document responds to the five remaining appeals submitted by the Dangerous Goods Advisory Council (DGAC), American Chemistry Council (ACC), Association of American Railroads (AAR), American Fuel & Petrochemical Manufacturers (AFPM), and jointly the Umatilla, Yakama, Warm Springs, and Nez Perce tribes (Columbia River Treaty Tribes) and the Quinault Indian Nation (Northwest Treaty Tribes).